[Ardour-Users] Multiple USB devices, Ardour, Alsa, and Jack

[Dewey Smolka]

Hello all,

I sure hope someone can help me out here because I'm losing my hair on this one.

I've got a home studio where I record using Ardour and Jack. The audio
interface is a Lexicon Omega (4 capture channels, 2 playback channels
via USB), which has been working perfectly through Jack via Alsa. Last
weekend I picked up a Lexicon MX200 reverb/multieffect unit and a
Behringer mixing console.

The MX200 has a USB port, but apparently it's only for control -- the
directions specify that it can be used under Windows/OSX as an
external plugin via VST or AU, but that requires the USB connection as
well as the audio connections to the interface. The Behringer mixer
came with a 2-channel-in 2-channel out USB interface that's recognized
and works under Alsa and Jack on its own.

For reference, I'm running UbuntuStudio 7.10 with kernel 2.6.22-14-rt.
It's the AMD 64-bit kernel so running the VST plugin via wine is not
an option.

What I'd like to do is to keep using the Omega as the primary
input/output device but be able to simultaneously use the MX200 as a
send/return loop using the USB interface that came with the mixer. As
I said, both the Omega and the simple USB interface work flawlessly as
long as they're on their own.

So far I haven't had any luck. Jack by itself can only address a
single device, and as Jack addresses Alsa, any solution will likely
have to happen between Alsa and the hardware layer. I considered using
PulseAudio as I read that it can merge multiple devices into a single
virtual device that can be managed by Alsa, but I was told on the
PulseAudio list that Jack wouldn't be able to address the virtual
device.

Someone on the PulseAudio list pointed me to jack_diplomat as a way of
running separate jackd sessions on each device and merging them as a
single session. I did manage to compile it and get the program running
and syncing the cards but I haven't been able to get Ardour working in
this setup. And I'm not sure that it's exactly ideal.

Most of what I've read about the possibility or impossibility of
running multiple cards simultaneously under Alsa has focused on the
idea of merging multiple cheap cards into a single capture/playback
device. The big problem as I understand is the fact that there's no
way to keep the clocks synced between the devices. I understand that
problem, but this isn't what I want to accomplish, and I'm not sure
how a bit of clock drift would be a problem for what I'm trying to do.
(I am, however, willing to accept the idea that I'm too married to the
analog way of doing things and don't understand the importance of the
word clock.)

My goal here is to be able to use all 4 capture channels and both
playback channels on the Omega for recording and monitoring in Ardour.
This I can do now without problem. At the same time I'd like to be
able to use the second USB interface as a send/return bus such that I
can set send levels by track which would all feed into a single return
bus, which would then be sent to the main mix and back out of the
Omega. That is, I'd like to be able to use both devices at the same
time, though they would never be operating in parallel.

I guess my main question is this: Is it possible to merge these
devices under Alsa such that Jack would be able to address both
devices simultaneously? I wouldn't ever be using the MX200 during
recording, but during mixdown I'd need to be able to send to the MX200
(secondary USB device), receive from the MX200, and send to the Omega
(primary USB device).

Please, please, someone tell me that what I want to do is possible.

Thanks in advance for any and all advice,

Dewey